<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        .father {
            background-color: #f23;

        }

        .son2 {
            background-color:blue; width: 200px;height: 200px;
        }

        .son1 {
            background-color: green;
            width: 100px;
            height: 100px;
            float: right;

        }
    </style>
</head>
<body>
<!-收缩指的是:
如果一个block元素 浮动之后它的宽度 就由内容决定了,而不是由父类容器决定
-->
<!--<div class="box1">aaaa</div>-->
<hr>
<div style="background-color:red; ">
<div style="background-color:green; width: 100px;height: 100px; float: right"></div>
<div style="background-color:blue; width: 200px;height: 200px;"></div></div>

</body>
</html>